Rotary kiln



R. D. PIKE ROTARY KILN June 24, 1930.

Filed May 6, 1926 INVENTOR.

78%: X9. WW.

Z 2 ww' ATTORNEYS.

Patented June 24, 1930 UNITED STATES BOBEBH! 1). 1mm, or PIEDMONT, cum-01mm I ROTARY KILN' J Application filed May 6,

My present invention relates to .rotary kilns, particularl those for burning Port land cement er, and has for its object toimprove both fuel economy and output '6 of a ln'ln of given-dimensions. It has special application as an improvement to the rotary kiln covered in my applicationfor Letters Patent Serial No. fi,103, filed May 3, 1926. As pointed out in the latter appli- 10 cation, the ratio of length to diameter has an essential bearing on the fuel; economy of rotary kilns. I have found that a kiln 225 feet long with internal diameter of 6 feet has an output of'700 barrels daily and a fuel 16 consumption of 1,020,000 B. t. u. per barrel of clinker weighing 365 pounds per barrel. By my present invention I am able to increase the output to substantially over 800 barrels per day and to reduce the fuel consumption to 800,000 B. t. 11. per barrel.

In the aforesaid 225' foot dry process rotary kiln with -6 feet internal diameter when-producing 700 barrels per day, the temperature of the gases on leaving the upper. end is about 1200 Fahrenheit; One example of the application of my present invention is to expand the diameter of some 30 feet of the upper end of the kiln by 2 feet; giving an internal diameter of 8.5 feet, and to place inside this'expanded zone of the shelLa plurality of longitudinally disposed cells formed of corrugated, heat-proof sheet metal. These ceIls are so disposed that the hot gases pass through each of them at sub stantially equal velocity, and the feed isabout evenly distributed to each at the upper or feed end, and is moved downwardly through each by the rotation of the kiln, until on reaching1 the lower end of the cells, it drops out of t em andback into the kiln, whence it pursues its course downwardly. This arrangement has the eifect of great y enlarging the surface for transmittal of heat to the raw mix in the upper end of the kiln, and results in the reduction of the temperature of the exit gas from 1200 Fahrenheit to about 800 Fahrenheit, and the increase in output and reduction in fuel con-' sumption aforesaid. My reason for expanding the diameter of the portion of the kiln 1926. Serial No. 107,016.

which houses the longitudinal cells is not only to. increase the space available for installing additional surface for heat trans-. mission, but also to reduce greatly the velocity of the gases, thus reducing their tendency to pick up dust. This latter is very important, because the raw mix as it drops out of the lower end of the cells is easily sus-' ceptible to being carried along in suspension by the stream of gas, provided the velocity ofthis gas is great enough. Some dust will be'pickedup at this point inv any event, and my method of returning it to the kiln, as described later, constitutes a novel feature of my invention.

I am well awarethat for many'years, in wet process kilns, it has been customary to install quadrants in the upper part of the kiln devoted to the evaporation of the Water from the slurry. These so-called quadrants divide the cross-section of the kiln into four segments and the \downcoming. slurry into substantially four streams.

Whatever benefit may be derived from this arrangement in wet process kilns, I have found it to be totally inadequate to accomplish the object sought by my invention, which primarily is the reduction of the temperature of the exit ases in the dry process example above given from,1200 Fahrenheit to about 800 Fahrenheit. In order to do this Ihave found it necessary to devise a novel means for providing the necessary area for heat transfer and 'for other purposes incidental to the main object of the invention. 7

In the accompanying drawing, I illustrate a typical exam 1e of my invention as applied toa kiln fiir burning Portland cement clinker.

Fig. 1 shows a general partial longitudinal section of the entire equipment;

Fig. 2 shows a central longitudinal sectional view of the section of the kiln adjacent the inlet end;

Fig. 3 shows a cross-section on the line I III--III of Fig. 2;

Fig. 4 shows a cross-section on the line having a lining 10 of refractory material. The shell in length is approximately 225 feet, and it is inclined downwardly from the inlet end to the discharge and approximately one-half inch per foot. The section Aadjacent the' upper or inlet end has an external diameter of 10 feet for about 35 feet. The intermediate section B for about 145 feet has an external diameter of 7 feet; and the section C adjacent the discharge end, fora length of about 45 feet is 7% feet in external diameter. Section A has a refractory lining 9 inches in thickness; section B has a refractory lining 6 inches inthickness; while section C has a lining 9 inches in thickness. Thus sections B and C internally are of the same internal diameter (i. e., ap-

proximately 6 feet).

The lengths specified include suitable taper lengths for rigidly connecting the sections of different diameters, and theusual' truncated conical or taper length at the upper end of the kiln. This shell is provided with the usual supporting tires 11 mounted rotatably in the cradles 12 and provided with a girth gear 13 driven by pinion 14 through driving mechanism not shown.- The upper end is provided with the usual rotating semi-airtight seal 15. Closure of the lower end of the kiln is effected by the usual firing hood 16, provided with a burner 17. The hot clinkers pass through the usual cooler 18 of rotary or other type, which serves to transfer heat from the clinker to the secondary air for combustion which en.- ters the firing hood through a port 19. e

Longitudinal cells 20-, 21, and 22 are formed in section A, each about 4 feet long, which when assembled form slipjoints wit each other,so as to provide continuous longitudinal cells for the entire length of the assembly. All'sections are alike except the' uppermost one 20' and lowermost one 22, which have differences to 'be described later. The intermediate cells 21 are formed of radial, corrugated plates- 23, made preferably of a heat-resisting fero-chrome steel, and corrugated, cylindrical sections 24 of the same material. The radial and cylindrical sheets, .atftheir' lines. of intersection, are securely fastened by riveting or Welding. At the center, also suitably secured to the radial plates, is a cylinder or pipe 25, of relatively small diameter. At their outer extremities the radial plates are flanged, so as to provide a mode of fastening to the inside of the steel plate shell of the kiln. This fastening may be effected either i by riveting; or welding. The aforesaid uppermost section 20 is provided for a portion of its lower length with concentric cylinders 24. .These 'latter are' omitted from a short portion of the kiln near the truncated conical feed end, leaving only the radial plates'27 projecting, -which,.

within a short distance of the inside surface of the kiln. y

The described arrangement of radial plates intersecting with cylinders provides a large number of longitudinal cells which ofier ample surface for heat transfer to the same number of separate streams of downwardly moving mix. The corrugations of the sheets are provided primarily to allow easy compensation for thermal expansion,

but they are also useful in increasing the effective area for heat transfer.

In assembling this structure the uppermst section 20 is placed first and secured to the.

shell of the kiln. Suitable temporary forms, not shown, are then placed, and the refractory lining rammed home. This latter may be made up of a mixtureof Portland cement and diatomaceous earth. The next lower section is then jointed .onto the first, so that the longitudinalcells register, secured to the shell and the refractory lining rammed home; and so forth until the entire assembly is placed. Considering the moderate temperature of the gases prevailing at the upper" end of the 225 foot rotary kiln, the described structure has a practically indefinite life.

The stack gases carrying dust pass into a chamber 30, and thence through the flue 31 into a dust collector 32. Exhaust fan 33 driven by motor 34, provides the draft and discharges the waste gases through a stack 35.' The recovered dust collects in the bottom of the collector and may be removed by any suitable form of dust pump 36, which .returns the dust through pipe 37 and delivprevents its being picked up by the draft a second time, and cuts down the dust circulation. The main feed for the kiln is stored in a feed box 38, and introduced into the kiln in the usual manner through a feed screw 39. If desired, the return dust from the collector 32 can also be fed in through this same feed screw.

It will be understood that the above example of my invention may be varied considerably in detail withoutdeparting from the spirit thereof, which involves broadly the application of adequate longitudinal heat-interchanging cellsin the upper end of a dry process rotary kiln, in which kiln the ratio of length to diameter is so adjusted that the gases entering the lowerend of the cellular passages are" at a sufliciently low Fahrenheit.

temperature so .as not to damage the structure ofthe cells. By means of my invention, -fuel economies hitherto considered impossible are attainable in rotary kilns, and a barrel of clinker can be produced for substantially 800,000 B. t. u. and the temperature of the stack ases reduced to about 800 bviously, it would be possible to employ this kiln for wet process; but in such event the invention loses significance, because the fuel consumption in wet process kilns cannot be reduced much, if any, below 1,400,000 B. t. u. per barrel if sufiicient heat is to be present in the upper part of the kiln for evaporating the water of the slurry.

When employing reference to the so-called ratio of length to internal diameter, the length referred to is the overall length of the kiln, and the diameter is the principal internal diameter without modification by the upper expanded length. For example, in the case illustrated the ratio is Having thus described my invention, what I- claim as new and desire to secure by Letters'Patent is:

l. A long, dry-process rotary cement kiln in which the ratio of length to the principal diameter'is not less than thirty to one, the

diameter ofsaid kiln being. enlarged atits upper end to comprise a pre-heating zone, spacedr'adial and circumferential partitions dividing said enlarged upper end into aplurality of longitudinal passages, said partitions bein gated metal.

2. An inclined rotary kiln for continuously treating a material having an inlet and an outlet at opposite ends thereof through which the material to'be treated is passed,

an enlarged section adjacent the inlet end' of said kiln provided with radially and circumferentially extending partitions intersecting each other and forming longitudinal passageways therein, said radially and circumferentially extending partitions being formed of corrugated: heat resisting metal.

3. An inclined rotary kiln of the character described having a. diametrically enlarged section at the upper end thereof divided into a plurality of longitudinally extending op sagewa; eing outlined by radially and circumferentially extending partitions of corrugated metal having a high heat conductivity and a high degree of heat resistance.

' ROBERT D. PIKE.

g formed of heat-resistant corruen-ended passageways, said pas- 

